1. Field of the Invention
The present invention relates to a moving object detector for detecting one or more moving objects on a screen by using an encoding parameter and an image monitoring system provided with the moving object detector.
2. Description of the Prior Art
In a prior art image monitoring system intended for crime prevention or disaster prevention using a surveillance camera, an enormous load is put on an observer because the observer should be stationed full time so as to check a monitor or the like at anytime, an enormous load is also put on a transmission path because of constant flow of coded streams through the transmission path, and a large amount of storage used for storing coded streams is needed because the coded streams are stored continuously. Therefore, in the prior art image monitoring system a moving object detector for automatically detecting one or more moving objects is adopted. Japanese patent application publication No. 9-252467 discloses an example as shown in FIG. 11 of such a moving object detector.
The prior art moving object detector shown in FIG. 11 is disposed on a side of a decoding apparatus, and is provided with a motion vector extraction unit 1102 for extracting a motion vector indicating an amount and direction of movement for each macroblock from a coded stream applied to the decoding apparatus, and a moving object determination unit 1103 for performing statistical processing on the amount and direction of the motion vector for each macroblock, which are extracted by the motion vector extraction unit 1102, and on positions and number of macroblocks associated with the motion vector so as to detect and keep track of one or more moving objects.
However, a problem with the above-mentioned prior art moving object detector is that since a motion vector is not necessarily extracted from each macroblock including a moving object according to an encoding mode determined for each macroblock during encoding of a moving image, it is impossible to accurately detect one or more moving objects by using only motion vectors. Particularly, since in an MPEG-4 video encoding system the moving image is encoded at a low bit rate and with a low resolution inmost cases, there may be cases where no motion vector is extracted from a macroblock including a moving object.
Furthermore, a problem with the above-mentioned prior art image monitoring system is that since coded streams are transmitted and stored even when no moving object exists in the monitoring site on the assumption that the observer should be stationed full time so as to check a monitor or the like at anytime and the moving image is continuously stored, an enormous load is put on the transmission path and a large amount of storage used for storing the coded streams is needed.
Another problem is that when a moving object is detected from a stored coded stream, it takes much time to search through the coded stream for data associated with the moving object.